In recent years, the semiconductor industry has been changing and progressing very fast. Accordingly, a semiconductor manufacturing apparatus that can further shrink the feature size and improve the throughput of elements has been sought. To meet the demand for a smaller element feature size, the numerical aperture (NA) of the lens has been increased. To manufacture high-performance elements with high productivity, an increase in the diameter of the substrate and the like have been performed.
For example, currently, an exposure system having two stages has been proposed to improve the throughput and alignment accuracy. This is an exposure system that transports and transfers a whole substrate holding unit between two stages as it holds a substrate. More specifically, according to this exposure system, alignment is performed at the first stage, and exposure is performed at the second stage different from the first stage during alignment. This makes it possible to ensure high-accuracy alignment time and improve the throughput.
To ensure the superiority of this system, first, the reproducibility of the surface of the substrate holding unit on different stages must be ensured reliably. More specifically, the substrate holding unit must be held between the first stage (alignment stage) and second stage (exposure stage) without changing the surface state of the substrate holding unit, e.g., the surface accuracy, distortion, or the like. Furthermore, the substrate holding unit must be moved between the stages quickly and must be stationarily held on or removed from a support surface for the substrate holding unit instantaneously.
In general, however, when the substrate holding unit and a support surface for it are to be brought into total contact with each other, it is difficult to stationarily hold the substrate holding unit on the support surface or to remove it from the support surface instantaneously. The substrate holding unit is highly likely to conform to the shape of the support surface for it. To reliably, stationarily hold the substrate holding unit, after it has moved from a stage, on the support surface for it, the substrate holding unit needs a stationary fixing force that can withstand stage driving. To ensure the reproducibility of the surface of the substrate holding unit at the second stage different from the first stage, when the substrate holding unit is to be moved between the stages or is to be stationarily held on or removed from the support surface for it, a power that changes the surface of the substrate holding unit should not be applied to the substrate holding unit. In a conventional exposure system, however, when the substrate holding unit is to be moved between the stages or is to be stationarily held on or removed from the support surface for it instantaneously, it is difficult to ensure the reproducibility of the surface of the substrate holding unit on different stages without changing the surface of the substrate holding unit.